Question
I have a yellow poplar I am concerned about ,It is drpping small branches and leaves and the leaves are turning yellow  with black spots, turning brown and dropping the leaves.

Answer
Tuliptree is one of the most common trees  that serve as "drought indicators" by dropping their yellowing interior leaves when their soil becomes too dry during summer drought. This is simply how they cope with drought, by cutting down on the number of transpiring "water leaks". If the summer is extremely hot and dry and adequate water is not supplied, Tulip Poplar can begin defoliating in late July. The spots are various leaf fungi that are common on poplar and do not effect the overall health of the tree.
Yellow poplar will shed small shaded branches as the die from the shade. This is normal and if the branches you are seeing are dead I would think this is from the lower interior branches that were shaded and the tree self pruned them. Nothing to worry about with them.